A rotor blade of a wind turbine, also referred to as a wind power plant or a wind energy converter, is a hollow structure having structural reinforcement members which are arranged inside the rotor blade. An outer surface of the rotor blade, which is mainly represented by a pressure side and a suction side, is not entirely supported by the structural reinforcement inside the rotor blade. Handling of a rotor blade has to be performed carefully to prevent the risk for damage of the rotor blade under its own weight. The rotor blade has to be grabbed at certain points or in certain area of the surface which are supported by the structural reinforcement members inside the rotor blade. In particular during installation of a rotor blade on a rotor hub of a wind generator, the rotor blade must be grabbed in these predetermined grabbing areas which are designed to support the weight of the rotor blade.
Two textile bands which are attached to a crane hook may be applied and represent the simplest tool for handling of the rotor blade. More complex handling devices allow a more flexible and convenient handling and positioning of the rotor blade. Such a device for handling of a rotor blade of a wind turbine is for example known from WO 2012/095112 A1. This rotor blade lifter comprises two grabbing jaws each having an antagonistic pair of arms carrying a plurality of pads for supporting the rotor blade. The pads contact a surface of the rotor blade in the predetermined grabbing areas.
Positioning of the handling device has to be performed precisely in order for the pads to grab the rotor blade exactly in the predetermined grabbing areas only. Today, the alignment of the lifter with respect to the rotor blade is performed by help of geometric measurements and/or by permanently visible positioning marks. A distance from the fixing flange of the rotor blade and a distance from the geometrical center of the rotor blade to a respective one of the grabbing areas is known from the manufacture of the rotor blades. The handling tool is adjusted with respect to the fixing flange and the geometrical center, for example by help of optical distance measurements of the permanently visible marks. This is however a rather complex procedure representing a time consuming step during handling of the rotor blade. Furthermore, a marking system comprising permanently visible marks, depending on the size of the marks, is not always in accordance with the blade marking standards, mainly related to air flight regulations.
The situation becomes even more complicated if a rotor blade should be removed from a wind generator. In particular for offshore wind generators, positioning of the handling tool may be hardly possible due to wind and motion of the sea even under ordinary weather conditions.